/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *  http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.mlizhi.base.codec.net;

import java.io.UnsupportedEncodingException;

import com.mlizhi.base.codec.DecoderException;
import com.mlizhi.base.codec.EncoderException;
import com.mlizhi.base.codec.binary.StringUtils;


/**
 * <p>
 * Implements methods common to all codecs defined in RFC 1522.
 * </p>
 * 
 * <p>
 * <a href="http://www.ietf.org/rfc/rfc1522.txt">RFC 1522</a> 
 * describes techniques to allow the encoding of non-ASCII text in 
 * various portions of a RFC 822 [2] message header, in a manner which
 * is unlikely to confuse existing message handling software.
 * </p>

 * @see <a href="http://www.ietf.org/rfc/rfc1522.txt">
 * MIME (Multipurpose Internet Mail Extensions) Part Two:
 * Message Header Extensions for Non-ASCII Text</a>
 * </p>
 * 
 * @author Apache Software Foundation
 * @since 1.3
 * @version $Id: RFC1522Codec.java 798428 2009-07-28 07:32:49Z ggregory $
 */
abstract class RFC1522Codec {

/**
 * Separator.
 */
protected static final char SEP = '?';

/**
 * Prefix
 */
protected static final String POSTFIX = "?=";

/**
 * Postfix
 */
protected static final String PREFIX = "=?";

/**
 * Applies an RFC 1522 compliant encoding scheme to the given string of text with the 
 * given charset. This method constructs the "encoded-word" header common to all the 
 * RFC 1522 codecs and then invokes {@link #(byte [])} method of a concrete
 * class to perform the specific enconding.
 * 
 * @param text a string to encode
 * @param charset a charset to be used
 * 
 * @return RFC 1522 compliant "encoded-word"
 * 
 * @throws EncoderException thrown if there is an error conidition during the Encoding 
 *  process.
 * @throws java.io.UnsupportedEncodingException thrown if charset is not supported
 * 
 * @see <a href="http://java.sun.com/j2se/1.4.2/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
 */
protected String encodeText(final String text, final String charset)
 throws EncoderException, UnsupportedEncodingException  
{
if (text == null) {
return null;
}
StringBuffer buffer = new StringBuffer();
buffer.append(PREFIX); 
buffer.append(charset);
buffer.append(SEP);
buffer.append(getEncoding());
buffer.append(SEP);
byte [] rawdata = doEncoding(text.getBytes(charset)); 
buffer.append(StringUtils.newStringUsAscii(rawdata));
buffer.append(POSTFIX); 
return buffer.toString();
}

/**
 * Applies an RFC 1522 compliant decoding scheme to the given string of text. This method 
 * processes the "encoded-word" header common to all the RFC 1522 codecs and then invokes 
 * {@link (byte [])} method of a concrete class to perform the specific deconding.
 * 
 * @param text a string to decode
 * @return A new decoded String or <code>null</code> if the input is <code>null</code>.
 * 
 * @throws DecoderException thrown if there is an error conidition during the Decoding 
 *  process.
 * @throws java.io.UnsupportedEncodingException thrown if charset specified in the "encoded-word"
 *  header is not supported 
 */
protected String decodeText(final String text)
 throws DecoderException, UnsupportedEncodingException  
{
if (text == null) {
return null;
}
if ((!text.startsWith(PREFIX)) || (!text.endsWith(POSTFIX))) {
throw new DecoderException("RFC 1522 violation: malformed encoded content");
}
int terminator = text.length() - 2;
int from = 2;
int to = text.indexOf(SEP, from);
if (to == terminator) {
throw new DecoderException("RFC 1522 violation: charset token not found");
}
String charset = text.substring(from, to);
if (charset.equals("")) {
throw new DecoderException("RFC 1522 violation: charset not specified");
}
from = to + 1;
to = text.indexOf(SEP, from);
if (to == terminator) {
throw new DecoderException("RFC 1522 violation: encoding token not found");
}
String encoding = text.substring(from, to);
if (!getEncoding().equalsIgnoreCase(encoding)) {
throw new DecoderException("This codec cannot decode " + 
encoding + " encoded content");
}
from = to + 1;
to = text.indexOf(SEP, from);
byte[] data = StringUtils.getBytesUsAscii(text.substring(from, to));
data = doDecoding(data); 
return new String(data, charset);
}

/**
 * Returns the codec name (referred to as encoding in the RFC 1522)
 * 
 * @return name of the codec
 */
protected abstract String getEncoding();

/**
 * Encodes an array of bytes using the defined encoding scheme
 * 
 * @param bytes Data to be encoded
 *
 * @return A byte array containing the encoded data
 * 
 * @throws EncoderException thrown if the Encoder encounters a failure condition 
 *  during the encoding process.
 */
protected abstract byte[] doEncoding(byte[] bytes) throws EncoderException;

/**
 * Decodes an array of bytes using the defined encoding scheme
 * 
 * @param bytes Data to be decoded
 *
 * @return a byte array that contains decoded data
 * 
 * @throws DecoderException A decoder exception is thrown if a Decoder encounters a 
 *  failure condition during the decode process.
 */
protected abstract byte[] doDecoding(byte[] bytes) throws DecoderException;
}
